1. Field
The present embodiments relate to attachments for attaching together a first body and a second body of a marine structure, which marine structure is adapted to be located at least partially immersed in water, wherein at least a portion of each one of the first and second body is adapted to, during use, to be in contact with the water. An attachment can comprise at least a portion of the second body, which comprises a wall which delimits the second body. An attachment can further comprise at least a portion of the first body, wherein the first body is fixedly attached to, and extends from, the second body.
The present embodiments further relate to methods of attaching together a first and second body of a marine structure. Further, the present embodiments relate to a semi-submersible vessel comprising an attachment according to the present invention.
2. Description of the Related Art
Marine structures are generally used for performing work and/or transports at sea or in lakes. For example, marine structures are used for drilling for, and production of, natural recourses such as gas or oil, when the natural recourses for instance are located in a well which is situated below the bottom of an ocean or a lake. Marine structures are also used for quartering personnel working at sea or on a lake.
As an example of marine structures, fixed production platforms may be mentioned, i.e. the type of platform constituted by a framework which is fixedly attached to a sea floor and extends upwardly through the water surface, or floating semi-submersible vessels which comprise a plurality of floats and/or columns. In order to enhance the strength of the marine structure, this is quite often provided with one or more bracings. For example, a semi-submersible vessel which is constituted by two pontoons and four columns may be provided with a bracing extending between the floats and/or the columns in order to make the ship more durable to external loads such as wave loads or internal loads such as for example the dead weight of the ship or pressure from liquids located on the ship.
Traditionally, a bracing is fixedly attached to the outer walls of the parts which are to be joined to one another and the fixed attachment is often achieved by means of a welded joint. Since the outer walls of the parts which are to be joined to one another by the bracing, in the example of a semi-submersible vessel the parts may for instance be pontoons and/or columns, often are adapted to be arranged at least partially immersed in water, often salt water, the weld joints are quite often located in a harsh environment. This makes great demands upon the weld joints and leads to expensive and complicated welding operations in order to achieve weld joints which fulfill the requirements of both extreme and fatigue strength, in particular since the weld joints are adapted to transfer large loads from the bracing to the outer walls. Furthermore, since the weld joints are located beneath the water surface, they may be difficult to inspect and/or repair, which results in that great demands also are made on the working life of the weld joints.
In order to solve this problem, the prior art proposes, for example U.S. Pat. No. 4,771,720, that the bracing is attached to an inner structure of a support column of a semi-submersible vessel. By this solution, a part of the load transfer from the bracing to the column occurs through a weld attachment which is located within the column and which is thus not exposed to the water ambient to the column. U.S. Pat. No. 4,771,720 also discloses that a portion of the bracing is attached to the wall of the column and this attachment is adapted to on the one hand be located in a harsh environment, namely immersed in water, and on the other hand transfer large loads from the bracing to the column. Thus, even if a reduction of the loads which are transferred through the weld attachment located in water is achieved in U.S. Pat. No. 4,771,720, it may still be difficult and expensive to design a weld attachment which is sufficiently strong as regards both extreme and fatigue strength. Furthermore, it is difficult to inspect the weld attachment which is located in water. Moreover, the attachment illustrated in U.S. Pat. No. 4,771,720 is especially suitable for marine structures under construction, or at least an attachment of a new bracing in an existing column.
Thus, a need exists for further improving the attachment of bracings in bodies of marine structures in order to enhance the strength of the joint, in particular as regards the fatigue strength.